Method and device for driving electrooptical light shutter

ABSTRACT

A method of and a device for driving a light shutter having an electrooptical effect to polarize an incident light by applying an electric field to the light shutter. When the light shutter is made activate, an excessive electric field in addition to a half-wave electric field which is a specific one to polarize an incident light at 90° in the static characteristics of the light shutter is applied to the light shutter initially, and subsequently, the half-wave electric field only is applied to the light shutter. To discharge the electric charge accumulated in the light shutter, no voltage is applied to electrodes each of which is provided on the wall of the light shutter so as to oppose each other subsequent to the application of the electric field until the next application thereof.

The application is a divisional of application Ser. No. 228,280 filedAug. 4, 1988, now U.S. Pat. No. 4,932,761 issued Jun. 12, 1990.

FIELD OF THE INVENTION

The present invention relates to a method of and a device for driving alight shutter employing a material, such as PLZT, having anelectrooptical effect, by applying an electric field to the shutter.

BACKGROUND OF THE INVENTION

Light shutters prepared from PLZT or like material having anelectrooptical effect are driven usually by the arrangement shown inFIG. 1. The illustrated light shutter 1 has electrodes 2 and 3 at itsopposite sides. With the electrode 2 grounded, a pulse voltage ofsuitable intensity is applied to the other electrode 3 as a drivevoltage Vd1, whereby light incident on the light shutter 1 through apolarizer 4 is polarized within the shutter 1 to pass through ananalyzer 5. The light is modulated depending on whether the drivevoltage Vd1 is thus applied to the shutter 1.

FIG. 2 shows the relationship between the voltage applied to the lightshutter of FIG. 1 and the intensity of light transmitted through theanalyzer. With such light shutters, it is known that the intensity oftransmitted light reaches a maximum level when a specific voltage isapplied at which the angle of polarization of the light within theshutter matches the analyzer in the static characteristics, that is,usually when a half-wave voltage Vλ/2 specific to the shutter 1 isapplied to polarize the light at 90°.

To drive the light shutter 1, therefore, the half-wave voltage Vλ/2 isconventionally applied to the other electrode 3.

In the case where the light shutter is used in electrophotographicprinters or the like, the shutter must be driven with pulses inconformity with the speed of rotation of the photosensitive drum forforming images thereon. However, if it is attempted to drive the shutterwith the half-wave voltage Vλ/2 in the form of pulses to givetransmitted light of maximum intensity, there arises the problem thatthe photosensitive drum can not be fully exposed to light and producesonly a poor contrast if the pulses are of short duration. For a fullexposure of the photosensitive drum, the half-wave voltage Vλ/2 needs tobe applied to the shutter in pulses of increased duration or width, butthis entails the problem of greatly reducing the system speed of theprinter or the like and failing to realize a high-speed operation.

On the other hand, when an array of a multiplicity of such lightshutters arranged in a line is used, for example, as the writing head ofan electrophotographic apparatus including a photosensitive member, withhalf-wave voltage Vλ/2 applied to one of the electrodes of one shutterto drive the shutter, the voltage applied to the electrode is high, sothat a current is likely to flow through another light shutter which isnot driven, permitting light to leak through the undriven shutter toimpair the contrast of the image obtained.

To overcome this problem, accordingly, we conceived utilization of thecharacteristics of the light shutter that with reference to thecharacteristics curve of FIG. 2, there is little or no transmitted lightuntil the voltage applied to the light shutter reaches a definite levelV1. For example, when the light shutter is 60 μm in the distance betweenthe electrodes at its opposite sides and 120 μm in the length of itsoptical path and is driven with a half-wave voltage Vλ/2 of about 50 V,there is substantially no transmitted light until the voltage reachesabout 20 V. More specifically, we prepared the arrangement of FIG. 3wherein a bias voltage Vb of up to the level V1 for giving notransmitted light was always applied negatively to the electrode 2 to begrounded, while a drive voltage Vd2, which was lower than the half-wavevoltage Vλ/2 by an amount corresponding to the bias voltage Vb, wasapplied to the other electrode 3 to drive the light shutter 1.

The potential difference across the electrodes 2, 3 at the oppositesides of this shutter 1 is the same as in the foregoing case wherein thehalf-wave voltage Vλ/2 is applied to one of the electrodes, such thatthe light shutter 1 is subjected to an electric field of the sameintensity as above and affords transmitted light of the same intensitywhile the drive voltage Vd2 to be applied to the electrode 3 can belower.

Nevertheless, we have found that in the case where the light shutter isthus driven, leakage of light still occurs even if the shutter is off asshown in FIG. 4.

SUMMARY OF THE INVENTION

Accordingly, the main object of the present invention is to provide amethod of and a device for satisfactorily driving a light shutter inaccordance with the characteristics of the shutter.

Another object of the invention is to provide a method of and a devicefor driving a light shutter having an improved speed of response so asto give a desired quantity of light within a shortened period of time.

Still another object of the invention is to provide a method of and adevice for driving a light shutter with a lower drive voltage free ofleakage of light.

To fulfill the above objects, the present invention is characterized byapplying to a light shutter an excessive electric field in addition to ahalf-wave electric field only initially when driving the shutter andsubsequently applying the half-wave electric field only to the shutter.

The invention is further characterized by applying voltages of differentpolarities to the respective electrodes of a light shutter to drive theshutter and thereafter discharging the charge accumulated in the shutterwith the applied voltages.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects or features of the present invention will becomeapparent from the following description of preferred embodiments thereoftaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram showing a common method of driving a light shutter;

FIG. 2 is a characteristics diagram showing the relationship between thevoltage applied to the light shutter and the intensity of transmittedlight;

FIG. 3 is a diagram showing a method of driving a light shutter byapplying a negative bias voltage to one of the electrodes for theshutter;

FIG. 4 is a diagram showing the relationship between the voltage appliedto the light shutter and the intensity of transmitted light when theshutter is driven by the method of FIG. 3;

FIG. 5 is a characteristics diagram showing variations in the intensityof transmitted light when a half-wave voltage Vλ/2 or the voltage Vλ/2plus an excessive voltage Vx is applied to the light shutter;

FIGS. 6 (a) and (b) are a side elevation and a plan view, respectively,schematically showing an electrophotographic printer incorporating alight shutter;

FIGS. 7 to 10 are diagrams showing variations in the intensity oftransmitted light when the respective different voltages used for FIG. 5are applied to the light shutter with a pulse width of 300 μsec;

FIG. 11 is a diagram showing the state of an electric field applied to alight shutter according to a first embodiment of the invention;

FIG. 12 is a diagram showing the intensity of light transmitted throughthe light shutter when the electric field of FIG. 11 is applied thereto;

FIGS. 13 (a) and 14 (a) are diagrams showing the state of voltagesapplied to the light shutter according to the first embodiment;

FIGS. 13 (b) and 14 (b) are electric circuit diagrams showing therespective drive devices for applying the voltages of FIGS. 13 (a) and14 (a) to the light shutter;

FIG. 15 is a characteristics diagram showing variations in the intensityof transmitted light when the light shutter of FIG. 1 is subjected to anelectric field, followed by discharging;

FIG. 16 is a characteristics diagram showing variations in the intensityof transmitted light when the light shutter of FIG. 3 is subjected to anelectric field, followed by discharging;

FIG. 17 is a characteristics diagram showing variations in the intensityof transmitted light when a negative bias voltage only is applied to oneof the electrodes of the light shutter of FIG. 3, followed bydischarging;

FIG. 18 is a circuit diagram showing a drive device according to asecond embodiment of the invention;

FIG. 19 is a timing chart for the operation of the drive device of FIG.18;

FIG. 20 is a diagram showing the relationship between the appliedvoltage and the intensity of transmitted light in the second embodiment;

FIG. 21 is a diagram showing the relationship between the appliedvoltage and the intensity of transmitted light in the second embodimentwhen the rise of the intensity of transmitted light is expedited;

FIG. 22 is a circuit diagram of the second embodiment as adapted todrive a light shutter array from block to block; and

FIG. 23 is a timing chart of the circuit of FIG. 22.

In the following description, like parts are designated by likereference numbers throughout the several drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First and second embodiments of the invention will be described below.

The principle of the first embodiment will be described first. FIG. 5shows variations in the intensity of transmitted light with time when ahalf-wave voltage Vλ/2, or the half-wave voltage Vλ/2 plus an excessivevoltage Vx is applied to the same light shutter as shown in FIG. 1, theexcessive voltage Vx being 10 V, 20 V or 30 V. Plotted as ordinate inFIG. 5 is the intensity of transmitted light (%) relative to theeventual intensity of transmitted light (peak in FIG. 2), taken as 100,due to the half-wave electric field Eλ/2, vs. the time (msec) plotted asabscissa. The diagram reveals that the higher the excessive voltage Vxapplied, the more rapid is the rise of the light intensity and thehigher is the speed of response, further indicating that the lightintensity gradually decreases with time as the voltage Vx increases.

Next, FIGS. 6 (a) and (b) show an array of light shutters like the oneshown in FIG. 1 and aligned, as incorporated in an electrophotographicprinter. The light from a halogen lamp 11 is led through a heatabsorbing filter 12 to a light guide 13, from which the light isincident on a rod lens 14. The light through the lens 14 is concentratedon the light shutter array 10, in which an electric field of requiredpulse width is applied to the light shutter element at an appropriateposition to transmit the light therethrough. The light passing throughthe light shutter element is collimated with an array of rod lenses, 15,in the form of a bundle of optical fibers and then projected onto aphotosensitive drum 16 to form a dot on the drum 16.

The period of time during which the light is on for forming the dot isup to hundreds of microseconds if longest, and this period decreases asthe system speed of the electrophotographic printer increases. FIGS. 7to 10 show variations in the intensity of transmitted light when thesame respective voltages as in the case of FIG. 5 are applied to thelight shutter with a pulse width of 300 μsec, on the assumption that theon period is 300 μsec. FIG. 7 shows such variations at the voltage ofVλ/2, FIG. 8 at the voltage of Vλ/2+10 V, FIG. 9 at the voltage ofVλ/2+20 V, and FIG. 10 at the voltage of Vλ/2+30 V. Plotted as ordinatein these diagrams are the drive voltage and the intensity of transmittedlight (%) relative to the eventual intensity of transmitted light, takenas 100, due to the half-wave voltage Vλ/2, vs. the time (μsec) asabscissa. The pulse of the drive voltage is indicated in broken line.The hatched portion in each diagram represents a cumulative quantity oftransmitted light.

Consequently, in the case where the on period is 300 μsec, theapplication of a voltage approximate to Vλ/2+20 V results in thegreatest cumulative quantity of transmitted light. Thus, this voltage,when applied to the light shutter, effectively exposes thephotosensitive drum to light.

When the light shutter array is driven with a pulse width of 100 μsec,it is desirable to use a drive voltage of Vλ/2+30 V or higher. Thus, asuitable excessive voltage Vx is used additionally in accordance withthe light-on period for forming dots.

As the electric field applied to the light shutter increases inintensity beyond the half-wave electric field Eλ/2 set up by thehalf-wave voltage Vλ/2, the rise of the intensity of transmitted lightis expedited, hence a higher speed of response, while the intensityraised remains stable when the shutter is thereafter driven with thehalf-wave voltage Vλ/2. Accordingly, this mode of voltage application isutilized for the first embodiment. Stated more specifically withreference to FIG. 11, the half-wave electric field Eλ/2 plus anexcessive electric field Ex as superposed thereon is applied to thelight shutter only initially when driving the shutter for the rise ofthe intensity of transmitted light, and the shutter is thereafter drivenwith the half-wave electric field Eλ/2 only without applying theexcessive field. The light intensity then rises rapidly and thereafterremains stable as seen in FIG. 12 to give a maximum cumulative quantityof transmitted light regardless of the light-on period. For reference,the broken line in the same diagram represents variations in theintensity of transmitted light when the light shutter is driven onlywith the half-wave electric field Eλ/2.

The light shutter can be driven in this mode by applying thereto a drivevoltage Vd which is the half-wave voltage Vλ/2 plus the excessivevoltage Vx superposed thereon, only when raising the light intensity asshown in FIG. 13 (a). FIG. 13 (b) is an electric circuit diagram showingan example of drive device for this purpose. With reference to FIG. 13(b), the voltage Vλ/2+Vx is applied to a terminal T1, and the voltageVλ/2 to a terminal T2. A periodic pulse signal S1 is applied to aterminal T3. In synchronism with this pulse signal S1, data for turningon and off the light shutter 1 is fed to a terminal T4. In the casewhere data for turning on the shutter 1 is fed, the voltage Vλ/2+Vx isapplied to one of the electrodes, 3, of the shutter 1 only during theduration of a pulse of the signal S1 initially, and the voltage Vλ/2 isapplied during the subsequent on periods. The other electrode 2 of theshutter 1 is grounded.

Alternatively, the light shutter may be driven with an electric fieldlike the one shown in FIG. 11 by applying a voltage Vd' shown in FIG. 14(a). In this case, the half-wave voltage Vλ/2 is applied to oneelectrode, and an excessive voltage -Vx of opposite polarity is appliedto the other electrode only initially. FIG. 14 (b) is an electriccircuit diagram showing a drive device for use in this case. Withreference to this diagram, the half-wave voltage Vλ/2 is applied to aterminal T5, and the excessive voltage -Vx to a terminal T6. A pulsesignal S1 and data like those described with reference to FIGS. 13 (a)and (b) are fed to terminals T7 and T8, respectively. Accordingly, whendata for turning on the light shutter 1 is fed, the voltage Vλ/2 isapplied to one electrode 3 of the shutter 1, and the voltage -Vx to theother electrode 2 initially, subjecting the shutter 1 to an electricfield Eλ/2+Ex. When the pulse signal S1 thereafter falls, the voltageVλ/2 only is applied to the shutter for an electric field Eλ/2 to actthereon.

The drive method and device of the first embodiment described abovegreatly improve the light shutter in speed of response to afford adesired quantity of transmitted light within a shortened period of time.

The second embodiment of the invention will be described next.

First, the principle of the second embodiment will be described. FIG. 15shows variations in the intensity of light transmitted through the samelight shutter as shown in FIG. 1 when the shutter is subjected to anelectric field with one electrode grounded and with a voltage applied tothe other electrode as in the case of FIG. 1, and also when the chargeis released from the shutter. FIG. 15 reveals that the variations in thelight intensity involve hysteresis characteristics. During the processwherein an electric field Eλ/2 is set up as the applied voltageincreases to the half-wave voltage Vλ/2, little or no transmitted lightis available until an electric field E1 is set up with a voltage V1,whereas during the discharging process, there is some transmitted lightpresent in the electric field E1 due to the voltage V1. Accordingly, thelight shutter was checked for variations in the intensity of transmittedlight by applying a negative bias voltage -Vb (≦-V1) to one electrode atall times and a drive voltage Vd2 (=Vλ/2-Vb) to the other electrode toset up an electric field as in the case of FIG. 3, and also by removingthe charge from the shutter. Consequently, it was found that when biasvoltage Vb only was applied to one electrode of the shutter, followed bydischarging, there was substantially no transmitted light as shown inFIG. 17. However, when the bias voltage Vb was applied to one electrodeand the drive voltage Vd2 to the other electrode, the light intensityexhibited hysteresis characteristics as seen in FIG. 16, such that evenafter the charge due to the drive voltage Vd2 was discharged, there wasleakage of light I_(OFF) under an electric field Eb due to the biasvoltage Vb.

With the second embodiment, therefore, the light shutter is driven byapplying voltages different in polarity to the electrodes of theshutter, and the charge accumulated in the shutter by the application ofthe voltages is entirely discharged.

FIG. 18 is a circuit diagram showing the second embodiment, in which thelight shutters 1 of a light shutter array 10 are provided withindividual electrodes 20 for the application of a drive voltage Vd2.These individual electrodes 20 are connected individually to a shutterdrive circuit 21. For the application of a negative bias voltage -Vb,the light shutters 1 have an electrically common electrode 22 which isconnected to a bias drive circuit 23.

A suitable light shutter 1 included in the array 10 is driven by thecircuit of FIG. 18 based on data. As seen in the timing chart of FIG.19, the data is fed to a shift register 24 and latched in a latchingcircuit 25. A strobing signal thereafter causes the shutter drivecircuit 21 to apply a pulse of drive voltage Vd2 to the individualelectrode 20 of the light shutter 1. In synchronism with the pulse ofdrive voltage Vd2, a pulse of negative bias voltage -Vb is applied tothe common electrode 22 by the bias drive circuit 23. After the suitableshutter 1 has been driven in this way, the charge accumulated in theshutter 1 with the drive voltage Vd2 and the charge with the biasvoltage -Vb applied to the common electrode 22 are discharged at thesame time.

The timing chart of FIG. 19 shows how the first shutter element 1a andthe second shutter element 1b are driven. First, a pulse of drivevoltage Vd2 is applied to the individual electrodes 20a, 20b of both thefirst and second shutter elements la, lb, and in synchronism with thepulse, a pulse of negative bias voltage -Vb of the same duration as thepulse of drive voltage Vd2 is applied to the common electrode 22,causing the first and second shutter elements 1a, 1b to transmit lighttherethrough. Subsequently, a pulse of drive voltage Vd2 is applied tothe individual electrode 20a of the first shutter element la withoutapplying any pulse to the individual electrode 20b of the second shutterelement 1b, and only a pulse of negative bias voltage -Vb applied to thecommon electrode 22 is cause to act on the second shutter element 1b.Thus, light is transmitted through the first light shutter element 1a,but no light through the second light shutter element 1b.

The bias voltage Vb to be applied t the common electrode 22 is madelower than the voltage V1 at which little or no transmitted lightthrough the light shutter is available as shown in FIG. 2 so that nolight leaks through the undriven light shutters 1 when the bias voltageVb is applied to the electrode 22 common to the light shutters 1. Thedrive voltage Vd2 to be applied to the light shutter 1 is so determinedthat the sum of the bias voltage Vb and the drive voltage Vd2 is equalto the half-wave voltage Vλ/2 at which transmitted light of maximumintensity is available.

When the pulse of drive voltage Vd2 is applied to the individualelectrode 20 of the light shutter 1 for passing light therethrough, andthe pulse of negative bias voltage -Vb of the same duration as the pulseof drive voltage Vd2 to the common electrode 22, the light shutter issubjected to an electric field equivalent to that set up by theapplication of the half-wave voltage Vλ/2 to afford the same quantity oftransmitted light as in the latter case as seen in FIG. 20. After thecharges accumulated by the drive voltage Vd2 and the bias voltage Vbhave been discharged, the shutter 1 transmits no light, hence no leakageof light.

In the case where the sum of the drive voltage Vd2 and the bias voltageVb is equal to the half-wave voltage Vλ/d, and these drive and biasvoltages are applied to the light shutter 1, the intensity oftransmitted light is slow to rise and requires some time to reach asufficient level as already described with reference to the firstembodiment

Accordingly, it is desired to expedite the rise of intensity of thelight through the light shutter by applying a raising negative voltage-VR of short pulse duration t initially when driving the shutter asshown in FIG. 21. With reference to FIG. 21, the raising negativevoltage -VR of short pulse duration t is applied along with the negativebias voltage -Vb in synchronism with the application of the drivevoltage Vd2 only initially when driving the light shutter, whereby theintensity of light through the shutter can be raised earlier to givetransmitted light of sufficient intensity within a shorter period oftime than in the case of FIG. 20.

Next, a description will be given of the case wherein a light shutterarray 10 comprising a multiplicity of light shutters 1 aligned isdivided into a plurality of blocks G and is driven from block to blockas seen in FIG. 22.

With reference to the circuit diagram of FIG. 22, each block G of thearray 10 has N light shutters 1_(l) 1_(N), and M such blocks G₁ to G_(M)are provided. The light shutters 1 are M×N in total number.

For the application of a drive voltage Vd2, N electrodes 20 areindividually provided for the N light shutters 1₁ to l_(N) in each ofthe blocks G₁ to G_(M) and are connected to N signal lines L_(l) toL_(N) in corresponding relation. On the other hand, an electrode 22 towhich a negative bias voltage -Vb is applied is formed for each block Gelectrically in common for the shutters 1 therein. The common electrodes22₁ to 22_(M) for the blocks G₁ to G_(M) are connected to analogswitches S₁ to S_(M), respectively, which are included in a multiplexer26.

To drive one block of the light shutter array 10, printing data is sentto a shift register 24 and then latched in a latching circuit 25, andthe shutter drive circuit 21 thereafter applies the drive voltage Vd2 tothe individual electrode 20 of the shutter 1 in the block through the Nsignal line L. On the other hand, the analog switches S₁ to S_(M) withinthe multiplexer 26 which are connected to the respective commonelectrodes 22₁ to 22_(M) of the blocks G₁ to G_(m) are so adapted that asuitable analog switch S only is actuated by a multiplexer controlcircuit 27. In synchronism with the pulse of drive voltage Vd2, a pulseof negative bias voltage -Vb is applied by a bias drive circuit 23 tothe common electrode 22 of the specified block G for which the analogswitch S is thus actuated, whereby the light shutter 1 in the block G isdriven.

Subsequently, in timed relation with the reduction of the drive voltageVd2 to zero, the voltage Vc on the common electrode 22 to which thenegative bias voltage -Vb is applied is nullified to zero to completelydischarge the charge accumulated in the light shutter 1.

A further description will be given with reference to the case whereinthe first block G₁ is driven. Only the analog switch S₁ for the firstblock G₁ is actuated as shown in FIG. 22. With reference to the timingchart of FIG. 23, the drive voltage Vd2 serving as a printing signal isapplied through the signal line L to the individual electrode 20 of asuitable light shutter 1 in the first block G₁, and in synchronism withthe application of the voltage Vd2, the negative bias voltage -Vb isapplied by the bias drive circuit 23 to the common electrode 22₁ of theblock G₁ to make the voltage Vcl on the common electrode 22₁ -Vb.

Consequently, an electric field due to the voltage Vd2+Vb acts acrossthe electrodes of the light shutter 1 in the block G₁ to which shutterthe drive voltage Vd2 is applied for the shutter to transmit lighttherethrough. On the other hand, the negative bias voltage -Vb only actson the other light shutters 1 of the block G₁, so that these shutterstransmit no light when the bias voltage Vb is set to a level lower thanthe voltage V1 at which almost no transmitted light is available asalready stated. Since the analog switches S₂ to S_(M) are off which haveconnected thereto the common electrodes 22₂ to 22_(M) of the otherblocks G₂ to G_(M), no electric field acts across the electrodes of theshutters 1 in these blocks to transmit no light therethrough.

After light has been transmitted through the suitable light shutter 1 inthe first block G₁ in this way, the voltage Vcl on the common electrode22₁ is reduced to zero in timed relation with the reduction of the drivevoltage Vd2 to zero to wholly discharge the charge accumulated in theshutter 1 and thereby completely turn the shutter off.

In the same manner as in the case of the first block G₁ described, lightshutters 1 in the second, third, . . . Mth block G₂, G₃, . . . G_(M) aredriven from block to block.

According to the second embodiment described above in detail, voltagesof different polarities are applied to the respective electrodes of thelight shutter to set a suitable potential difference across theelectrodes. In this case, the drive voltage to be applied to one of theelectrodes of the light shutter can be lower than when the shutter isdriven by applying voltage to only one of the electrodes. Thisdiminishes the damage to the switching element for the on-off control ofthe shutter, permits use of a switching element of lower voltageresistance and serves to provide the shutter at a reduced cost, henceadvantages. The low drive voltage to be applied to one of the electrodesof the light shutter eliminates the likelihood of leakage of lightunlike the prior art, consequently giving images of high contrast.

Furthermore, the charges accumulated in the light shutter with thevoltages applied to the respective electrodes are completely discharged,with the result that the light shutter as discharged is free of anyvoltage. This obviates the likelihood that light will leak through theshutter under the action of bias voltage and serves to provide images ofhigh contrast.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to be notedthat various changes and modifications will be apparent to those skilledin the art. Therefore, unless otherwise such changes and modificationsdepart from the scope of the invention, they should be construed asbeing included therein.

What is claimed is:
 1. A method of driving a light shutter having anelectrooptical effect to polarize an incident light by setting up anelectric field between electrodes of the light shutter, comprising:afirst step of applying voltages of different polarities to therespective electrodes of the light shutter when polarizing the incidentlight, and applying one of the voltages only to the respective electrodewhen not polarizing the incident light; and a second step of applying novoltage to the respective electrodes of the light shutter subsequent tothe first step so as to discharge the electric charge accumulated in thelight shutter; wherein the voltages applied to the respective electrodeswhen polarizing the incident light in the first step set up an electricfield, exceeding a half-wave electric field that polarizes said incidentlight by 90° according to the static characteristics of the lightshutter, and wherein subsequently, said voltages set up the half-waveelectric field only.
 2. A driving device for a light shutter having anelectrooptical effect to polarize an incident light by applying anelectric field to the light shutter, comprising:a first and secondelectrodes each of which is provided on the wall of the light shutter soas to oppose each other; and a control circuit connected to at least oneof the first and second electrodes for applying to the light shutter anexcessive electric field in addition to a half-wave electric field whichis a specific one to polarize an incident light at 90° in the staticcharacteristics of the light shutter initially when activating the lightshutter, and subsequently, for applying the half-wave electric fieldonly to the light shutter; and wherein the first electrode is connectedto the control circuit, and the second electrode is grounded; andwherein the control circuit has a first terminal applied with a firstvoltage for setting up the excessive electric field in addition to thehalf-wave electric field, a second terminal applied with a secondvoltage for setting up the half-wave electric field only, a thirdterminal applied with a periodic pulse signal, a fourth terminal appliedwith data for turning on and off the light shutter in synchronism withthe periodic pulse signal and switching means for selectively applyingone of the first and second voltages to the first electrode in responseto the periodic pulse signal and data.
 3. A driving device as claimed inclaim 2, wherein the first voltage is applied to the first electrodeduring the duration of the periodic pulse signal when the on-data ispresent, and the second voltage is applied thereto during the timeperiod subsequent to the duration of the periodic pulse signal when theon-data is present, by means of the switching means.
 4. A driving devicefor a light shutter having an electrooptical effect to polarize anincident light by applying an electric field to the light shutter,comprising:a first and second electrodes each of which is provided onthe wall of the light shutter so as to oppose each other; and a controlcircuit connected to at least one of the first and second electrodes forapplying to the light shutter an excessive electric field in addition toa half-wave electric field which is a specific one to polarize anincident light at 90° in the static characteristics of the light shutterinitially when activating the light shutter, and subsequently, forapplying the half-wave electric field only to the light shutter; andwherein both of the first and second electrodes are connected to thecontrol circuit; and wherein the control circuit having a first terminalapplied with a first voltage for setting up the half-wave electricfield, a second terminal applied with a second voltage of the polaritydifferent from that of the first voltage for setting up the excessiveelectric field, a third terminal applied with a periodic pulse signal, afourth terminal applied with data for turning on and off the lightshutter in synchronism with the periodic pulse signal, and switchingmeans for selectively applying the first and second voltages to thefirst and second electrodes, respectively, in response to the periodicpulse signal and data.
 5. A driving device as claimed in claim 4,wherein the first and second voltages are applied to the first andsecond electrodes during the duration of the periodic pulse signal whenthe on-data is present, and the first voltage only is applied to thefirst electrode during the time period subsequent to the duration of theperiodic pulse signal when the on-data is present, by means of theswitching means.
 6. A driving device for a light shutter having anelectrooptical effect to polarize an incident light by applying anelectric field to the light shutter, comprising:first and secondelectrodes each of which is provided on the wall of the light shutter soas to oppose each other; a first control circuit connected to the firstelectrode for applying a first voltage thereto; a second control circuitconnected to the second electrode for applying a second voltage of apolarity different from that of the first voltage thereto; and a thirdcontrol circuit for controlling the first and second control circuitsaccording to data for turning on and off the light shutter so that whenan ON-data is present, the first and second voltages are applied to thefirst and second electrodes to make the light shutter turn on and a zerovoltage is applied to both electrodes subsequent to the applications ofthe first and second voltages, when an OFF-data is present the firstvoltage only is applied to the first electrode to maintain the lightshutter turned off; wherein both of the first and second voltagesapplied to the first and second electrodes set up an electric field,exceeding a half-wave electric field that polarizes said incident lightby 90° according to the static characteristics of the light shutter,when the light shutter is initially turned on to polarize the incidentlight, and wherein subsequently, said voltages set up the half-waveelectric field.
 7. A driving device for a light shutter array having aplurality of light shutter elements aligned with one another, each ofthe light shutter elements having an electrooptical effect to polarizean incident light by applying an electric field thereto, the devicecomprising:a plurality of individual electrodes each of which isprovided on the wall of the respective light shutter element; a commonelectrode which is provided on the opposite walls of the respectivelight shutter elements electrically in common so as to oppose to theindividual electrodes; a first control circuit to which the individualelectrodes are connected individually for selectively applying a firstvoltage thereto at a periodic timing; and a second control circuitconnected to the common electrode for applying a second voltage of apolarity different from that of the first voltage thereto at theperiodic timing; wherein the first voltage is altered within the oneapplication period so as to initially set up an electric field,exceeding a half-wave electric field that polarizes said incident lightby 90° according to the static characteristics of the light shutterelements, and to subsequently set up the half-wave electric field only,while maintaining the second voltage constant, in order to make thelight shutter element turn on.
 8. A driving device for a light shutterarray having a plurality of light shutter elements aligned with oneanother, each of the light shutter elements having an electroopticaleffect to polarize an incident light by applying an electric fieldthereto, the device comprising:a plurality of individual electrodes eachof which is provided on the wall of the respective light shutterelement; a common electrode which is provided on the opposite walls ofthe respective light shutter elements electrically in common so as tooppose the individual electrodes; a first control circuit to which theindividual electrodes are connected individually for selectivelyapplying a first voltage thereto at a periodic timing; and a secondcontrol circuit connected to the common electrode for applying a secondvoltage of a polarity different from that of the first voltage theretoat the periodic timing; wherein the second voltage is altered within theone application period so as to initially set up an electric field,exceeding a half-wave electric field that polarizes said incident lightby 90° according to the static characteristics of the light shutterelements, and to subsequently set up the half-wave electric field only,while maintaining the first voltage constant, in order to make the lightshutter element turn on.
 9. A driving device for a light shutter arrayhaving a multiplicity of light shutter elements aligned with one anotherand divided into a plurality of blocks, each of the light shutterelements being having an electrooptical effect to polarize an incidentray of light by applying an electric field thereto, the devicecomprising:a multiplicity of individual electrodes each of which isprovided on the wall of the respective light shutter element; aplurality of common electrodes arranged block by block, each of which isprovided on the opposite walls of the respective light shutter elementsincluded in the respective block electrically in common so as to opposeto the individual electrodes; a first control means, to which theindividual electrodes are connected so as to be in common with the lightshutter elements located in different blocks, for selectively applying afirst voltage to the individual electrodes at a periodic timing, blockby block; and a second control means for applying a second voltage of apolarity different from that of the first voltage to the commonelectrode of the block to be driven at that timing, and for switchingoff the electrical connection of the common electrodes of the blocks notto be driven at that timing; wherein the first voltage is altered withinthe one application period so as to initially set up an electric field,exceeding a half-wave electric field that polarizes said incident lightby 90° according to the static characteristics of the light shutterelements, and to subsequently set up the half-wave electric field only,while maintaining the second voltage constant; in order to make thelight shutter element turn on.
 10. A driving device for a light shutterarray having a multiplicity of light shutter elements aligned with oneanother and divided into a plurality of blocks, each of the lightshutter elements having an electrooptical effect to polarize an incidentray of light by applying an electric field thereto, the devicecomprising:a multiplicity of individual electrodes each of which isprovided on the wall of the respective light shutter element; aplurality of common electrodes arranged block by block, each of which isprovided on the opposite walls of the respective light shutter elementsincluded in the respective block electrically in common so as to opposethe individual electrodes; a first control means, to which theindividual electrodes are connected so as to be in common with the lightshutter elements located in different blocks, for selectively applying afirst voltage to the individual electrodes at a periodic timing, blockby block; and a second control means for applying a second voltage of apolarity different from that of the first voltage to the commonelectrode of the block to be driven at that timing, and for switchingoff the electrical connection of the common electrodes of the blocks notto be driven at that timing; wherein the second voltage is alteredwithin the one application period so as to initially set up an electricfield, exceeding a half-wave electric field that polarizes said incidentlight by 90° according to the static characteristics of the lightshutter elements, and to subsequently set up the half-wave electricfield only, while maintaining the first voltage constant, in order tomake the light shutter element turn on.